The present invention relates to the positioning of getters within a cathode-ray tube. More particularly, this invention relates to a getter placement and attachment assembly for securing and positioning getters along the major axis of a cathode-ray-tube (CRT).
During the manufacture of a CRT, the ultimate vacuum is obtained through the use of getters that are primarily barium compound materials. Barium is flashed or vaporized by placing an RF coil near the outside wall of the CRT funnel adjacent the getter after the tube has been exhausted and sealed, where the RF energy from the activated coil vaporizes the getter material. The vaporized getter material absorbs and reacts with the residual gas molecules in the picture tube and removes them as low vapor pressure solid condensate and continues to absorb any further liberated gases throughout the life of the CRT.
It is a common practice to position the getter in the inside surface of the neck and yoke portions of the CRT attached to the electron gun. Since the getter holder containing the getter material must be outside the path of stream of electrons directed from the electron gun toward the viewing screen of the tube, and since the diameter of the funnel cross-section at the neck and yoke portions of the CRT is relatively small, it is known to locate the getter in the forward region of the tube envelope on screen related structures, such as the shadow mask frame or the exterior surface of the internal magnetic shields (IMS). Furthermore the position of getters in the neck and yoke regions of the tube are detrimental to operating tubes at the higher scan rates required for high performance tubes. Therefore, it is desired to remove the getter source from the neck and yoke regions, while still maintaining good getter pumping characteristics.
Cases in which the getters are attached to the exterior surface of the IMS, the IMS may have any number of configurations including imperforate structures so that the flashed getter material is accessible to the residual gas molecules within the CRT. However, this position of the getter on the exterior surface of the IMS can nevertheless result in getter flash deposit on the backside of the IMS thereby restricting the deposit of getter material from reacting with the gas molecules within the tube. Attaching the getter in the forward region of the tube, as in the case of the shadow mask frame, also reduces getter flash distribution due to its close proximity to the viewing screen of the tube. Consequently, an increase in localized gas pressure occurs and positively charged ions are generated by the collision between the electron beams and the gas molecules within the tube. The positively charged ions are accelerated toward the cathodes of the electron gun, where they bombard and deplete the cathode coatings, resulting in a reduction of cathode emission.
The problem associated with getter flash distribution is further aggravated in a larger size CRT. As the size of the CRT increases, a relatively larger amount of active barium material to react with the residual gas molecules is required. Moreover, as the aspect ratio of the CRT increases, the major or horizontal axis of the CRT increases thereby increasing the distribution distance of the flashed getter along the major axis of the CRT. Increased amounts of barium material may be placed within the CRT with larger or multiple getter holders, however, this configuration results in increased getter flash deposits on undesired areas of the CRT as described above, i.e., getter flash tends to deposit on the back side of the IMS. On the other hand, reducing the number of getters and positioning the getter holder to achieve a getter flash distribution that substantially avoids the IMS and neck regions of the tube also reduces the getter performance because the flashed getter material does not maintain a sufficiently low pressure within the CRT by absorbing the residual gas molecules therein. The lack of vacuum pressure within the CRT envelope is essential for adequate life of the CRT.
Thus, it is desired to have a getter placement and attachment assembly that provides optimum getter flash distribution within a CRT to permit the flashed getter material to react with the residual gas molecules within the CRT without depositing on undesired areas of the CRT.
The present invention relates to a getter placement and attachment assembly for securing and placement of the getter along the major axis of a CRT. The present invention provides optimum getter flash distribution within a CRT and finds particular utility in large size and large aspect ratio CRTs in which relatively large areas of getter distribution is desired.
As will be set forth in greater detail in the description of the preferred embodiment, the getter placement and attachment includes a getter spring for removably securing the getter to an internal magnetic shield affixed to the frame of the color selection electrode or mask frame of a CRT. The internal magnetic shield has sidewall enclosures with a plurality of apertures therethrough along the major axis of the CRT to permit optimum deposition of a getter film within the CRT.